The invention is directed to a thyristor and more particularly to a thyristor with a reduced breakover voltage.
When, in a thyristor, the voltage that is applied between the cathode electrode and the anode electrode, and that blocks the thyristor, is increased to the value of what is referred to as the breakover voltage, then a local breakdown occurs of the pn-junction that separates the p-base from the n-base and proceeds about parallel to a principal face of the semiconductor body. In general, the breakdown appears at that edge of this pn-junction that lies in the lateral surface of the thyristor. In order to avoid such a uncontrollable local breakdown that very often leads to the destruction of the thyristor, European Pat. Publication No. EP-A-O 088 967 discloses that the pn-junction between the p-base and the n-base may be provided with a projecting part that reduces the thickness of the n-base, formed, for example, by means of irradiation with a laser beam under the central ignition contact of the thyristor, and to thus produce a breakdown at a reduced breakover voltage, this breakdown appearing in the region of the projecting part. This breakdown leads to an over voltage ignition of the thyristor so that a thermic destruction does not occur as a result of the reduced breakover voltage. What is disadvantageous, however, is that the reduced breakover voltage cannot be set to a defined voltage value with the desired precision and reproducibility.